1. Field of the Invention
This invention relates to a method and device for applying electric currents to glow plugs of diesel engine cylinders, so as to ensure smooth start of such engines especially automobile engines. More particularly, the invention relates to regulation of the power consumption in the glow plugs by switching the connection of the glow plugs from parallel to serial and vice versa so as to couple either the parallel-connected or serial-connected glow plugs to a power source such as a car battery.
2. Description of the Prior Art
It has been practiced to regulate the power consumption in glow plugs of engine cylinders, for instance by using a high power consumption in the glow plugs during the preheat period and reducing the power consumption in them during the after-glow or keep-warm period following the preheat. In fact, the inventors disclosed a method for regulating the glow plug power consumption in their Japanese Patent Laying-open Publication No. 192,972/1983, in which the connection of the glow plugs to a power source is changed between parallel and serial. As compared with a conventional method of inserting a current-limiting resistor means in series to the glow plugs after finishing the preheating thereof, the above method of the inventors has a merit of reducing the waste in the power consumption.
However, the method of the prior art has a shortcoming in that satisfactory engine starting characteristics and the engine warming up characteristics cannot be achieved, because the glow plug temperature control of the prior art does not provide optimal glow plug temperature separately for different operating periods such as the preheating period, the cranking period or the starter motor running period, and the after-glow period following the engine start.